1. Field of the Invention
This invention relates to an optical arrangement with a light source and an optical element, and more particularly to projection exposure systems for microlithography, in which a thermal effect that is not rotationally symmetrical that results from the irradiation from the light source is compensated. Microlithography notoriously is the art of producing structures in the micrometer and submicrometer range—inter alia for microelectronic devices—by photolithography.
This situation is of particular importance in wafer scanners with a slit-shaped image field: either a narrow rectangle slit with a width to length ratio of e.g. typically 1:5 to 1:9, or an arcuate shape, particularly in mirror systems.
2. Discussion of Relevant Art
Active compensation of the imaging errors resulting from asymmetric thermal effects is known from European Patent EP-A 0 678 768, and its corresponding application U.S. Pat. No. 5,803,273 to Unno by regulated or controlled non-rotationally-symmetrical heating or cooling and also, by way of a suggestion, by mechanical stressing.
The like was described earlier in European Patent EP-B1 0 532 236, preferably as heating for mirrors.